Gut microbiota structure differs between honey bees in winter and summer

Honey bees harbor a relatively simple and highly conserved gut microbiota. Yet, little is known about the dynamics of the bee gut microbiota across seasons, especially in winter when adult worker bees live much longer and are critical for colony survival. We quantified the major community members of the bee gut microbiota in a single colony over two years and monitored 14 additional colonies during summer and winter. Our data shows that the total abundance of the gut microbiota in nectar/honey-feeding foragers was significantly lower compared to pollen-feeding nurses and winter bees. Strikingly, long-lived winter bees had the highest bacterial loads, with a characteristic shift towards a predominance of Lactobacillus Firm-5 and Bartonella apis . By colonizing microbiota-depleted bees with a community reconstituted from bacterial isolates, we provide experimental evidence that diet is a major contributor to the observed differences in bacterial loads between winter bees, nurses, and foragers. Overall, our study reveals that the gut microbiota of winter bees is remarkably different compared to foragers and nurses. Considering the importance of winter bees for colony survival, future work should focus on the role of the gut microbiota in health and disease in winter bees.